Application of automated segmentation algorithms in MRI studies means that WM volumes are calculated incidentally by the majority of studies appearing in the literature. By itself, mention of tissue segmentation into GM, WM, and CSF was not sufficient for inclusion in the meta-analysis; reports were required to investigate WM volume as a variable of interest in AUDs. This criterion was met when the study either reported means and standards deviations for WM volume or performed a test of group differences in WM volume. In 3 cases (Gazdzinski et al., 2010; Gazdzinski et al., 2005; Lee et al., 2007) where WM volume differences had been tested but sufficient data to calculate the ES were absent (e.g., test statistics reported only as non-significant), the corresponding author was contacted for more information.
